A South Jersey police officer testified Monday that Bordentown Police Chief Frank Nucera Jr. routinely used racial slurs and compared blacks to ISIS and said President Trump “is the last hope for white people.”

The explosive testimony came in the second week of Nucera’s hate-crime assault trial in U.S. District Court in Camden. The now-former chief is also charged with a civil rights violation and lying to the FBI.

The prosecution’s star witness, Sgt. Nathan Roohr, a K-9 officer in the Burlington County department, said Nucera grabbed the head of Timothy Stroye “like a basketball” and slammed it into a metal door jam during an encounter at a Bordentown hotel. Stroye, a handcuffed black suspect, was in police custody.

The impact, Roohr said, “made a loud thud.”

”I immediately knew it was wrong. I knew I had an obligation to report it,” Roohr said. “This was an obvious excessive force.”

Roohr later notified federal authorities about the Sept. 1, 2016 episode and a probe was launched. Prosecutors say Nucera, the longtime chief, had a “significant history“ of making racial remarks.

Police were summoned to the Ramada Hotel by a manager who said Stroye, then 18, of Trenton, and his girlfriend, 16, had not paid for a room and were swimming in the pool. Both teens got into an altercation with police and backup officers arrived, including Nucera.

After the assault, authorities say, the chief made a series of racist remarks back at the station that were secretly recorded by Roohr and played for the jury Monday. Roohr made 81 tapes of his former boss during the investigation. Other officers on the 25-member force also recorded Nucera.

In a snippet played Monday, Nucera could be heard saying: “It’s gonna get to the point where I could shoot one of these [expletives].”

In the same conversation, Nucera complained about the 2016 presidential race and his fear that Democratic candidate Hillary Clinton would ”give in to all the minorities.”

“Donald Trump is the last hope for white people,” Nucera said on the recording.

Roohr, who is still on the force, said the racist remarks by the former chief actually began several years earlier. He said he became more vigilant in turning on the audio recorder on his cell phone after the ISIS comments Nucera made in 2015.

Roohr read from a note he said he wrote after Nucera spewed the N-word. He said the chief was upset after the tires on a police car were slashed, and Nucera suspected a black defendant.

“These [N-word] are like ISIS, they have no value. They should line them all up and mow 'em down. I’d like to be on the firing line, I could do it,” Roohr quoted Nucera as saying.

During his testimony, Roohr, a 16-year veteran of the department, did not make eye contact with his former boss. Nucera, sitting at the defense table, occasionally looked up at Roohr.

Experts say the case is unusual because Roohr broke the “blue wall of silence.” His identity, kept secret by prosecutors in their criminal complaint against Nucera in October 2017, eventually was revealed in court documents filed by the defense.

Nucera’s lawyer, Rocco Cipparone, has questioned Roohr’s motives in recording Nucera and suggested there was a concerted effort to get Nucera off the force by officers dissatisfied with his overtime policies and disciplinary actions. Nucera makes no admission on the recordings to roughing up the suspect in the assault, he said.

Roohr said Nucera directed K-9 officers to use police dogs to intimidate black spectators at high school basketball games against predominantly black competitors and at an apartment complex with a large minority population.

”Let these {expletives} see him. Let ‘em see him. I don’t care,” Nucera said in a recording.

Jurors, many wearing headphones to hear the recordings, listened intently during Roohr’s nearly three hours on the stand Monday. His testimony will resume Tuesday. The trial before Judge Robert Kugler is expected to last about two more weeks.

The jury also heard testimony from Lt. Shawn Mount, one of the first officers to arrive at the Ramada. He said he used pepper spray after Stroye disobeyed commands and grabbed his gun belt.

Stroye was charged with resisting arrest, assault on an officer, and theft, but a judge later dismissed the charges. Stroye told police he couldn’t identify the person who struck him.

Nucera resigned from the department and a dual role as the administrator of the township of 11,000 in January 2017 after learning he was being investigated.

If convicted, Nucera could face up to 20 years in prison and forfeit his $8,800 a month pension. He is free on bond.