The son of a Boston police captain was an ISIS supporter who planned to set off an improvised explosive device and was arrested after illegally purchasing four firearms on July 4, according to a Justice Department press release and MyFoxBoston.

Authorities say 23-year-old Alexander Ciccolo, who also went by the name Ali Al Amriki and posted about martyrdom on Facebook, spoke about setting off an explosive device “in places where large numbers of people congregate, such as college cafeterias.” He was seen purchasing a pressure cooker similar to the kind used by the perpetrators of the Boston Marathon bombing.

Ciccolo’s father reported his son to the FBI after noticing suspicious behavior, according to MyFoxBoston.

"According to a close acquaintance, the defendant had a long history of mental illness and in the last 18 months had become obsessed with Islam," the Justice Department’s detention memo stated.

The Ciccolo family released a statement Monday thanking authorities for preventing any casualties and asking the public for privacy.

"While we were saddened and disappointed to learn of our son's intentions, we are grateful that authorities were able to prevent any loss of life or harm to others. At this time, we would ask that the public and the media recognize our grief and respect our desire for privacy," the statement read.

Ciccolo first planned to attack members of the military and law enforcement personnel, according to conversations he had with a confidential informant, as related in DOJ documents.

Later he expressed a desire to attack an unidentified university in another state, with the attack broadcast live online. He allegedly wanted to complete his attack no later than July 31 and was aware he could be killed in the operation.

"We win or we die," he’s quoted as saying in the detention memo.

The FBI arrested Ciccolo after he took possession of the guns, which were given to him by the confidential informant. Ciccolo was previously arrested for an alcohol-related crime and was ineligible to buy the firearms.

A subsequent search of Ciccolo’s apartment turned up partially constructed molotov cocktails, two machetes and a large knife.

After his arrest, authorities allege Ciccolo stabbed a nurse in the head with a pen during a medical exam, “leaving a bloody hole in the nurse’s skin and causing the pen to break in half.”

The case was sealed until Monday, though the Department wouldn’t comment on why.

Ciccolo is scheduled for a detention hearing on Tuesday and is behind held in custody until then.

The arrest appears to lend credence to FBI Director James Comey's claim that the Bureau prevented multiple credible plots during the Independence Day holiday.