Two Boston men were arrested yesterday and another is being sought in connection with the shooting death of a Middlesex Country assistant district attorney last fall, county officials said yesterday.

Howard Whitehead, first assistant district attorney for Middlesex County, said yesterday the three have been charged with the murder of Edward Bingham 3rd, who was fatally wounded on October 2 as he sat in his parked car on Memorial Drive near the MIT campus.

Whitehead identified the suspects as Henry McLendon, Aldin Carter and Arnold Evans, all Boston residents in their early 20s. All three face charges of murder, two counts of armed assault with intent to rob, and assault with a dangerous weapon.

State police Lt. William Kelly said yesterday the suspects had been under surveillance for months, adding that "We really had to work for this one."

Bingham, 28, was shot in the chest after three men approached his car. Marion Ryan, another assistant district attorney, who was with Bingham at the time of the shooting, said Bingham shielded her with his body. Ryan suffered powder burns from the gunshot.

Whitehead said that Robert Banks, first assistant district attorney from Norfolk County, would serve as special prosecutor in the case.

"We didn't feel we could treat the case with the kind of detachment one really ought to have in a prosecution," Whitehead said, adding, "One of our attorneys will be testifying in the case and we don't want to arouse any charges of conflict of interest."