Charges brought, then withdrawn in double shooting

Boston police announced yesterday that they had found the shooter who tried to kill two boys in Mattapan over the weekend.

Little more than an hour later, they said they had the wrong man.

Tyshawn Woodley, 19, of Dorchester, had a good alibi: He was with a police officer at the time of the shooting, the Suffolk district attorney's office said, announcing that the charges had been dropped.

After a witness accused Woodley and after obtaining a warrant, police tracked him down on Monday evening and arrested him in the shooting of the two boys, ages 15 and 16, on Glenarm Street about 10 p.m. Saturday.

According to police, Woodley insisted he was innocent, saying he was at a police station on Blue Hill Avenue at the time of the attack.

Still, officers went ahead and charged Woodley with two counts of assault and battery with a dangerous weapon and assault with intent to murder. Both victims in the case had been treated at Boston Medical Center for wounds that were not life-threatening .

Prosecutors said further investigation confirmed Woodley's alibi. "As a result, the defendant could not have been involved in the shooting incident," prosecutors said in their request to the court to terminate the case "in the interests of justice."

Elaine Driscoll, a spokeswoman for the Police Department, said an officer from the gang unit who had stopped Woodley before the shooting had taken him to the station.

Asked whether police filed the charges prematurely, she said the standards for probable cause were met.

"This is a case where our internal systems worked very well," Driscoll said. " Most importantly, the officers disclosed exculpatory evidence immediately to stop the prosecution." She added, "This is an example of good police work."

The shooting on Glenarm Street was the first of two attacks Saturday night. A half-hour later, on Wilmore Street in Mattapan, gunfire hit a 9-year-old girl and two boys, also ages 15 and 16.

The shootings occurred amid changes in the Police Department criticized by Suffolk District Attorney Daniel F. Conley. The prosecutor asserted that by replacing the head of the department's homicide unit, Commissioner Edward F. Davis might blunt progress in investigations. Conley also was displeased that he wasn't consulted in advance about the change.

Detectives from the B-3 station arrested Woodley. They are supervised by Deputy Superintendent Thomas Lee, who is taking over the homicide unit.

David Abel can be reached at dabel@globe.com.