Philadelphia Police Commissioner Richard Ross made two points crystal clear during 90 minutes of testimony Thursday: The Police Department is not an arm of federal immigration enforcement, and it does not intend to start behaving that way.

Ross was the first and most prominent witness called to the stand in U.S. District Court in the city's lawsuit against Attorney General Jeff Sessions, lodged over the Trump administration's attempt to withhold grant money from "sanctuary cities."

The commissioner testified that Philadelphia police arrest people who commit crimes without regard for their citizenship status. A criminal, he said, is a criminal. At the same time, the department depends on information and help from law-abiding citizens, he said, and part of that trust is built on the fact that police do not routinely collect and store data on whether individuals are in this country illegally.

"There's no way in the world you'd want to come forward as a source of information or criminal activity if you learned you would be deported," Ross said.

Broadly defined, a sanctuary city limits its cooperation with federal authorities that enforce immigration law. City leaders generally aim to ease fears of deportation among undocumented residents, believing that members of immigrant communities will then be more willing to report crimes.

President Trump and Sessions have argued that sanctuary city policies allow dangerous criminals to be released into local neighborhoods, when they should be returned to their homelands.

Philadelphia filed its suit in August. Chicago, Los Angeles, San Francisco, and California also are going to court over the new restrictions on a federal grant that supports police training and overtime, among other improvements. The lawsuits accuse the president and attorney general of withholding the money as a cudgel to make cities enforce federal immigration laws.

Last year, Philadelphia received $1.67 million.

In July, Sessions added two additional requirements for the grants. At the request of officials with Immigration and Customs Enforcement, cities must give agents two days' notice before releasing undocumented inmates from custody. In addition, they must allow ICE agents to enter any detention facility to question immigrants about their right to be or stay in the United States.

The city contends that those requirements were not authorized by Congress and that they violate the 10th Amendment by forcing local governments to do the work of federal authorities.

No immediate ruling was expected in the case, with further testimony scheduled for next week.

Philadelphia city officials, including Ross, say they avoid the term sanctuary city because it's difficult to define. Instead, they say, they implement policies that provide equal treatment to all who enter the criminal justice system.

On Thursday, Justice Department lawyer Arjun Garg pressed Ross and other witnesses about the circumstances under which local police might assist ICE in its work.

In his testimony, Ross drew a  line between ICE requests for information on people who have broken the law, as opposed to those who are victims or witnesses. In the former, when asked, the city may provide information about immigration status, if it has it. In the latter, Ross said, the police will provide no information, believing confidentiality to be crucial to cooperation between police and residents.

Victims and witnesses to crimes must know they can come forward without concern that police will investigate their status, Ross said. Without that assurance, "some of our partners in the neighborhood would fear us, and we can't afford to have that happen. It would severely inhibit our ability to get info, intelligence."