A California woman reportedly noticed “suspicious activity” at a house connected one of the Muslim terrorists in the San Bernardino massacre but did want “profile” him, amid questions about how family members and others could have overlooked the stockpile of ammunition and explosives left behind in his home.

A man identified as Aaron Elswick told an ABC News affiliate that a fellow neighbor noticed “quite a few packages” being delivered “within a short amount of time” at a home registered to the mother of Syed Farook, who with wife Tashfeen Malik, fatally shot 14 people and wounded dozens of others Wednesday at a business complex in San Bernardino, Calif.

The Islamic State-inspired Malik reportedly entered the country on a so-called “fiancé visa” that listed a false or at least inaccurate foreign home address.

Elswick said his neighbor also noticed the occupants of the home purportedly owned by Farook’s mother “doing a lot of work out in the garage” but perhaps “didn’t want to profile” Farook and his family.

The revelation follows investigators’ reports after the deadly shooting that they found roughly 4,500 rounds of ammunition, 12 pipe bomb-type devices, and bomb-making tools inside Farook and Malik’s Redlands, Calif., apartment and garage.

The couple lived there with their 6-month-old daughter and purportedly Farook’s mother.

“I think his mother knew,” front-running Republican presidential candidate Donald Trump said Saturday at a campaign event in Iowa. “I think anybody who walked into that apartment knew.”  

He also said people should report suspicious behavior “but racial profiling should not be going on. … We have to use common sense.”

Lawyers for Farook's mother and three siblings described Malik as "just a housewife" who was quiet like her husband and strictly followed Muslim custom.

In addition to the discovery inside the couple’s apartment, investigators found more than 1,400 rounds of .223 caliber ammunition and more than 200 9-mm rounds in their rented vehicle, after they were killed in a shootout with police, said San Bernardino Police Chief Jarrod Burguan.

Also this weekend, the FBI raided the Riverside home a man suspected of buying the “assault-style” weapons the couple used in the attack. However, no arrest was made, and investigators do not suspect the ex-neighbor, Enrique Maraquez, was directly involved in any sort of plot or terrorism activity.  

A law enforcement official says that more than three years ago, the person who lives in the house, whom the Associated Press reported was a friend of Farook's, bought two assault rifles later used in the shooting, but authorities haven't been able to talk to him because he checked himself into a mental hospital after the attack. The official was not allowed to discuss the investigation publicly and spoke on condition of anonymity.

The attack was the nation’s deadliest mass shooting since the Newtown, Connecticut, school tragedy three years ago that left 26 children and adults dead.

In Malik’s visa application, she listed an address in her home country of Pakistan. This summer, she received her Green Card, which allows immigrants to legally live and work in the United States, according to ABC News.

The Department of Homeland Security did not respond Saturday to a Fox News request for comment.

The issue raises questions about the vetting process for immigrants into the United States, amid growing concerns that Middle East terrorists could be slipping into the country.

Farook traveled to Saudi Arabia and returned to the United States with Malik in July 2014. They were married the next month.

Farook reportedly had contact with people connected to at least two foreign terrorist organizations -- Al Qaeda-affiliated Nusra Front and the African extremist group Al-Shabaab -- before the attack.

Islamic State radio also released a statement early Saturday saying two supporters of the terror group committed the San Bernardino killings, according to Reuters. 

However, ISIS has not claimed responsibility for the attacks.

Reports about Farook’s potential ties to terror groups and the Islamic State follow news that 29-year-old Malik had pledged her allegiance to ISIS before and after the attacks, suggesting the couple was driven by radical Islam.

Prior to Malik’s move to the United States, she studied pharmacy at Bahauddin Zakariya University in the Pakistani city of Multan. Whether she graduated remains unclear.

A maid who worked in the Multan home where Malik lived said she would travel back to Saudi Arabia to be with her family when school was out. During her stay in Multan, her style of dress became more conservative over time, the maid said.

Authorities told The Los Angeles Times that authorities in Pakistan are investigating whether Malik had ties to radical Islamist organizations.

There have been reports Farook had ties to radicals in Pakistan and had a made a trip there in recent years. But a source connected to the Pakistani Consulate in Los Angeles told Fox News on Friday that Farook didn’t possess a Pakistani passport. And there is no record of him applying for a visa to travel to Pakistan through his local consulate.

However, Farook could have entered that country illegally.

The FBI acknowledged Friday that it is treating the shooting investigation as an act of terrorism.

"This is now a federal terrorism investigation," said FBI Director James Comey.

David Bowdich, the assistant FBI director in charge of the Los Angeles office, said neither Malik nor Farook was on law enforcement's radar prior to the attack.

However, he acknowledged they attempted to cover up their digital trail, damaging hard drives and other electronic devices.

In addition, investigators found two cell phones in trash cans near the couple's Redlands home and evidence of communications with others who are now being investigated in connection with the attack.

Some information continues to trickle in about Malik, but a large part of her life remains a mystery. A leader of the area’s Pakistani-American Muslim community said the woman had “no presence on the Internet" and didn't interact with others in the Muslim community.”

Malik and Farook married in Riverside County, Calif., according to their marriage license. The marriage and passage of criminal and national security background checks using FBI and Department of Homeland Security databases resulted in the conditional green card for Malik in July 2015, two months after she gave birth to the daughter.

Farook is a third-generation American from a family hailing from Karachi, Pakistan. Sources close to his family say his marriage to Malik was not arranged.

Farook is a devout Muslim who prayed every day and recently memorized the Koran, said his brothers, Nizaam and Rahemaan Ali.

Rahemaan Ali said he last saw Farook three weeks ago, when he abruptly stopped going to the mosque. Ali said Farook seemed happy and his usual self, and the brothers never saw a violent side.

Prior to Farook’s marriage, he had multiple online dating profiles claiming he was a Sunni Muslim from a “religious but modern family” and that he was “looking for a girl who has the same outlook, wear hijab, but live life to the fullest, be my partner for snowboarding, to go out and eat with friends, go camping, working on cars with me.”

Co-workers said Farook was reserved. They said he had grown his beard out in recent months -- often a sign among Muslims of heightened religious devotion.

He also had gotten into several heated arguments with a co-worker, Nicholas Thalasinos, about Islam. Thalasinos reportedly questioned whether Farook’s faith was truly a “religion of peace.” He was one of the 14 killed in Wednesday’s attack.

Neither Malik nor Farook had a criminal record, and the couple did not mix with the larger Pakistani-American community. Few people, including neighbors, claimed to have seen Malik, or to have even met her. The Pakistani-American Muslim community leader, who asked that his name not be used, said the community believes that someone radicalized Farook.

The Associated Press contributed to this report.