A half-dozen FBI agents yesterday converged on the Bronx apartment building where four cops gunned down Amadou Diallo, photographing and measuring the crime scene in an attempt to piece together the shooting.

Agents were at 1157 Wheeler Ave. at the request of Manhattan U.S. Attorney Mary Jo White.

The FBI carefully examined the bullet-scarred door and walls inside the Soundview building, painstakingly recording the measurements of the vestibule where Diallo was shot Feb. 4.

The FBI's involvement came as the U.S. Commission on Civil Rights asked Attorney General Janet Reno to investigate the shooting.

Police said Diallo was hit with 19 of 41 shots fired by four street crime cops as the unarmed man stood in the vestibule of his apartment building at 12:45 a.m.

Federal authorities in New York have monitored the case as the Bronx district attorney presents evidence to the grand jury, which heard its second day of testimony yesterday.

The grand jury is expected to spend three weeks hearing evidence before voting on whether to indict the officers on charges that could range from murder to criminally negligent homicide.

One of Diallo's two roommates, as well as Emergency Medical Service personnel, testified yesterday, sources said.

The cops — Edward McMellon, 26; Kenneth Boss, 27; Sean Carroll, 35, and Richard Murphy, 26 — have not said whether they will testify.

Marilyn Mode, a police spokeswoman, said the four cops surrendered their firearms Monday.

In Brooklyn, a prayer service coincided with Diallo's burial in his homeland of Guinea, and local clergy staged a prayer vigil outside Bronx Supreme Court — a daily ritual slated to continue while the grand jury meets.

The Rev. Wyatt Tee Walker led three dozen supporters in the vigil. "These four men ought to be indicted for second-degree murder," he said.