The strategy sounds almost illogical: Detectives in New Jersey are being urged to build criminal cases with as few witnesses as possible. Or, if feasible, with none at all.
In cities struggling with gang-related crimes, such as Trenton and Newark, detectives said that even on those infrequent occasions when they have found witnesses who might be willing to testify, investigators were wary about pressuring them to appear in open court. That reluctance is based on a fear that the authorities might not be able to protect witnesses from retaliation.
In the New Jersey State Police gang unit, the approach is so common that detectives have made hundreds of cases during the past five years but used civilian testimony fewer than a dozen times, investigators said.
Even Gov. Jon S. Corzine has directed police agencies in the state to use witnesses more sparingly in cases involving street gangs.
Detective Sgt. Ronald Hampton of the state police, who has worked in the gang unit since 2002, said the testimony of civilian witnesses is considered evidence of last resort.
"It used to be that when someone gave information, the first words out of a detective's mouth were, 'Are you willing to testify to that?'" Hampton said.
But no more.
"If you push someone and they agree to testify, now they're your responsibility," he said. "You've got to keep them from disappearing or getting hurt. Can we protect them? Maybe. But God forbid that two years later, you have to tell someone their husband or father got killed. I don't want to have to live with that."
No one much disputes that the strategy amounts to something of a retreat for law enforcement in New Jersey. But as homicides have climbed across the state - and with more than a dozen witnesses having been killed in the past five years - building what might be called "witness-less cases" is seen as defensible. And necessary.
Cases are made using video surveillance or sting operations, or police testimony only. But those tactics can carry a cost for the public. The cases that can be made without witnesses - often drug sales or gun possession cases - tend to carry shorter sentences than more serious crimes.
Critics said that by resorting to methods that allow gang members to reduce, or avoid, punishment for their crimes, the police are essentially rewarding them.
In Maryland, where witness intimidation has ranged from acts of vandalism to homicide, legislators have changed state law to prosecute intimidators. Attorneys have also used taped interviews with witnesses, although not all of these trials have led to successful prosecutions.
Sun reporter Liz F. Kay contributed to this article.