New Haven police arrested their first murder suspect of the year last week but saw much of that progress evaporate as a wave of eight shooting incidents has swept across the city since, leaving one dead.

That murder, the city’s 12th this year, brings the number of unsolved homicides back up to 11.

Around 2 a.m. Saturday morning, police officers maintaining order at the closing of Humphreys Bar and Restaurant on the edge of the East Rock neighborhood were confronted by a bigger challenge when they heard gunshots nearby. Not more than 50 feet away, inside a Chevrolet Tahoe, the officers found Edmund Jackson, 25, shot to death through the chest at close range.

The officers could not find the shooter and as yet have no suspects, matching the pattern for this year’s homicides.

Saturday’s murder is part of a violent spree in New Haven that started last October and has claimed 12 lives so far this year, equal to the total number of homicides in all of 2009. Police had made no arrests in any of the killings until last Wednesday morning, when detectives arrested William Wilkins, 21, and charged him with an April 10 murder.

But that same afternoon, the new rash of violence began.

Shortly before 5 p.m. that same day, witnesses saw an armed man chase after and shoot repeatedly at another man in a foot chase in the Hill neighborhood. Since then, seven other shooting incidents, including Jackson’s murder, have occurred in the city’s traditional high-crime neighborhoods of Dixwell, Newhallville, and Dwight-Chapel.

Police have only recovered shell casings in the shootings, which police say may be used to trace ballistics evidence back to perpetrators. But in some cases not even shells have been recovered, and ballistics has yet to prove useful in solving the rest of this year’s shootings.