A former CIA contractor who kept 60 notebooks full of classified information will spend three months in prison.

Why Reynaldo Regis over his 10 years at the agency felt compelled to look up classified information about individuals outside his purview and take it home with him, however, remains a mystery.

“The $64 question is why he was keeping those notebooks,” U.S. District Judge Liam O’Grady said Friday before sentencing Regis in an Alexandria courtroom.

After hearing from the prosecutor, defense attorney and Regis himself, the judge concluded, “The why is not going to be answered here.”

Regis, a Philippine native who spent 25 years in the U.S. military and held a top-secret security clearance, only told O’Grady, “I’m really sorry for what I have done . . . truly sorry.”

Part of Regis’s job at the CIA was to research people in classified databases, according to court papers. But throughout his decade there, he also conducted unauthorized searches and read classified information from highly sensitive intelligence reports.

Prosecutors said Regis, of Fort Washington, Md., recorded “several hundred instances” of that classified information in notebooks over the past decade that he would take out of agency headquarters in his personal bag, drive home in his car and keep in his house.

The notebooks were found in a Nov. 3, 2016, search of Regis’s car and home. While the search was being conducted, Regis lied to FBI agents, claiming that he had never taken classified information home.

“He had no nefarious purpose,” defense attorney Cary Citronberg said after the sentencing. “It was just a mistake.”

Regis got credit for undergoing about six debriefing sessions with the CIA, explaining what searches he conducted and where he stored the classified information, according to court documents, “in order to allow them to conduct necessary risk assessments and protect their information against any inadvertent spills.”

Regis will also serve three years of supervised release, and prosecutors asked that the CIA be notified if he wants to leave the country.

Sentences in such cases vary widely. A National Security Agency employee who brought work on sensitive hacking tools home was recently sentenced to five years in prison by a federal judge in Maryland. But retired Army general and former CIA director David Petraeus and former national security adviser Sandy Berger both got probation for taking home classified information.

“We go where the facts take us,” Assistant U.S. Attorney Danya Atiyeh said in court.

An earlier version of this article incorrectly referred to the National Security Agency as the National Security Administration.