A man accused of negotiating ransoms on behalf of Somali pirates used his cell phone to search for information about four Americans days before they were killed in their yacht off the coast of Africa in February, the U.S. government revealed in court filings.

The details about Mohammad Saaili Shibin's arrest in Somalia and interrogation by U.S. officials were contained in the government's response to a defense claim he was unlawfully questioned aboard a government plane.

The government responded Monday that the FBI "studiously followed the law of interrogation" and that Shibin was "fully capable of understanding his rights and making an informed and voluntary decision regarding whether to speak to the agents without an attorney present."

Shibin is charged with piracy, kidnapping and weapons charges for his alleged role in the February hijacking of the yacht Quest. He has pleaded innocent.

Prosecutors have said Shibin never boarded the Quest, but operated from Somalia to determine how much ransom the hostages could fetch. He is considered the highest-ranking suspected pirate the United States has prosecuted.

The government filing in U.S. District Court in Norfolk describes Shibin as a 50-year-old former oil worker who speaks English, Arabic and some Italian. He was a translator and dispatcher before he was laid off by African Oil Corp., the government said.

Shibin acknowledged negotiating the release of a German ship for several million dollars in December 2010 and receiving a $30,000 payment for it, prosecutors said.

The Quest's owners, Jean and Scott Adam of Marina del Rey, Calif., and friends Bob Riggle and Phyllis Macay of Seattle were killed several days after being taken hostage hundreds of miles south of Oman as the Navy attempted to negotiate their rescue.

The Navy told the pirates that they could keep the yacht in exchange for the hostages, but they refused to take the deal because they didn't believe they would get enough money. Ransoms are typically millions of dollars.

According to court documents, one of the pirates fired a shot above Scott Adam's head and told him to tell the Navy that if they came any closer, the Americans would be killed. Soon after, one of the pirates fired a rocket propelled grenade at the USS Sterett, where two other pirates were on board conducting the negotiations, the court records show.

The four Americans were being held in the yacht's steering wheelhouse on Feb. 22 when they were killed without provocation, according to court records.

They were the first U.S. citizens killed in a wave of pirate attacks that have plagued the Gulf of Aden and the Indian Ocean in recent years, despite an international flotilla of warships that patrol the area.

FBI investigators who questioned Shibin in early April showed him screen shots from his cell phone that included Internet searches for the Quest and the Adamses on Feb. 19-20, days after the sailing vessel was hijacked but before they were killed, according to the government court filing, which alleges that Shibin researched the hostages and the Quest on the Internet to determine the ransom.

The screen shots included queries on their telephone numbers, profiles of the couple and the value of the Quest.

"Shibin claimed that he had researched the Quest solely out of curiosity," prosecutors wrote. "He further stated that he knew about the hijacking of the Quest, but he was never interested in negotiating for its return or release."

During the questioning, he told agents he had an auto-alert feature on his phone that informed him when hijackings occurred around Somalia.

The government was responding to a pretrial filing by Shibin's attorney, James Broccoletti, who is seeking to suppress statements made by Shibin. He is also seeking dismissal of the piracy count because he argues that Shibin's alleged land-based actions did not include robbery at sea.

In a separate response filed Tuesday, the government said the motion should be dismissed under landmark U.S. law and evolving international law defining piracy.

"How Shibin could possible think that his efforts to facilitate the high seas hijacking of a vessel and the detention of the persons on board for purposes of extracting a ransom from their family members was not illegal — and illegal piracy specifically — is a question that his motion fails to answer," prosecutors wrote.

Shibin's trial is scheduled for Jan. 31. Eleven others in the case have already pleaded guilty to piracy and three others are facing murder charges. The eleven men who pleaded guilty agreed to help prosecutors in this case and possibly others in exchange for the possibility that their mandatory life sentences might be reduced.