TRENTON, N.J. (AP)  -- A woman's testimony against the drug dealer next door helped put him away for life. Now a fire has consumed her home and killed her 10-year-old girl, and police say the convicted man's associates may have set it.

Investigators found evidence suggesting arson in the blaze that killed Qua-Daishia Hopkins on Sunday, and Trenton Police Director Joseph Santiago said the case was being investigated as possible witness retaliation homicide. If that proves true, it would be the third such death in the city this year.

The girl's mother, Francis Hopkins, had testified against a man who was convicted last year of running a crack house next to their home, according to police.

Prosecutors at Isaac ``Chin'' Barlow's trial said there was evidence he was trying to locate witnesses so he could ``get rid of them.''

While Barlow is now serving life in prison, police are investigating whether he arranged from behind bars for gang members to carry out an attack on the Hopkins' home.

Fifty officers began canvassing the city Monday, offering a $25,000 reward for tips in the investigation.

At a Tuesday press conference, the police director and Trenton Mayor Douglas Palmer called for changes to court rules and New Jersey law to protect witnesses from retaliation.

``We cannot allow criminals to subvert our justice system,'' said Palmer. ``They are undermining our entire society.''

Palmer said lawmakers should immediately pass a law elevating witness intimidation to a first-degree offense.

Santiago said the identities of witnesses should be concealed until trial. He also called for higher bail on gun possession charges in order to give police more leverage against gang activity.

In the last decade, detectives in Trenton have been much less successful with homicide investigations, Santiago said, due in part to the reluctance of witnesses to cooperate.