The central piece of physical evidence from the plot to bomb the Herald Square subway station is a handscrawled map of Staten Island, which police found in the pocket of a young Pakistani immigrant, Shahawar Matin Siraj.

The map, prosecutors said, shows that long before Mr. Siraj, 23, plotted to bomb the subway station, the conspiracy for which he is being tried, he considered a plot to target the police precincts of Staten Island, or the four bridges linking the island to New Jersey and Brooklyn.

But Mr. Siraj, who lived in Queens, did not draw the map. The map comes from the hand of a former friend, James Elshafay, a 21 year-old from Staten Island who took the witness stand yesterday in U.S. District Court in Brooklyn to testify against Mr. Siraj.

Elshafay, who has been diagnosed as schizophrenic, pleaded guilty to the Herald Square bomb plot conspiracy in October 2004. Since then, the government has not commented on his case. He faces five to 20 years in prison. Neither Elshafay nor Siraj was believed to have possessed any explosives.

When asked by a lawyer, Khurrum Wahid, why he pleaded guilty, Elshafay responded with a simple answer: “Because I’m guilty.”

Elshafay testified yesterday that he was sexually abused during a childhood that consisted of truancy, drug use, anti-Semitic rages, and delusions, involving voices. At about the age of 12, as a boy and under the sway of his father’s stories of fighting in the Egyptian military against Israel in 1973, he distributed 20 copies of a flier posing a question: “Did you beat a Jew today?”

Although raised a Catholic, Elshafay testified that he gravitated towards Islam, the religion of his father, around the age of 17. Following a trip to Egypt in the summer of 2002, he began to visit an Islamic bookstore in Bay Ridge, where he became friends with the defendant, Mr. Siraj, who worked there as a clerk.

Over the next two years, Elshafay testified that he studied Islam, learning from Mr. Siraj and an older man, who turned out to be a police informant named Osama Eldawoody. Mr. Siraj’s attorneys have argued that Eldawoody, who was on the NYPD payroll, entrapped Mr. Siraj and encouraged him to go ahead with the plot to bomb the subway station.

“At the time I thought it was Islamically obligatory,” he said when lawyers asked him about the Staten Island plans. He said he has since left Islam, and prays from his prison cell with the aid of Jewish prayer books.