Los Angeles Police Chief William Bratton, said on Tuesday that the los Angeles Police Department (LAPD) must stay out of the business of collaring illegal immigrants if it wants to keep solving crimes.

Bratton, who ends his seven years as chief on Saturday, urged his eventual successor to continue a three-decade-old policy known as Special Order 40. It prohibits officers from stopping people solely to determine whether they are in the country illegally.

"My officers can't prevent or solve crimes if victims or witnesses are unwilling to talk to us because of the fear of being deported," Bratton said in an opinion piece in the Los Angeles Times.

Bratton said police were able to arrest a suspect in the March murder of a homeless man because an undocumented immigrant, who witnessed the attack, came forward.

In 2006, Harold Sturgeon filed a lawsuit against the department on behalf of taxpayers, claiming the 1979 policy violates state and federal law by prohibiting full cooperation between police and Immigration and Customs Enforcement agents.

A California Court of Appeals panel upheld the policy in June. Bratton said some residents have asked why the LAPD has not joined a Homeland Security programme, known as 287(g), that gives some local and state police officers the powers of federal immigration agents. Dozens of agencies have joined in the controversial programme.

Bratton said getting the public to report crimes and identify criminals helps improve community relations.