Law enforcement officials in New York on Tuesday continued preparing for possible unrest on the streets of Manhattan as a grand jury investigating Donald Trump over a hush money payment to the adult film-maker and star Stormy Daniels appeared poised to complete its work by criminally indicting the former president. Barriers were brought to the area around the Manhattan criminal courthouse in the lower part of the island. Uniformed police were out in force. So were reporters and protesters. People holding placards bearing anti-Trump messages chanted: “No one is above the law.” One pro-Trump protester was seen with a sign saying the Manhattan district attorney, Alvin Bragg, was funded by George Soros. Soros, a progressive philanthropist, gave money to an advocacy group which supported Bragg for election. The protester’s sign echoed, if while misspelling “George”, Republican attacks on “Soros-funded prosecutors” which itself echoes antisemitic invective. Last weekend, Trump claimed without evidence he would be arrested on Tuesday. His representatives later said he was citing media reports and leaks and there was no indication his prediction would come true. The grand jury did appear to take an important step on Monday by hearing from a witness favourable to Trump, presumably so prosecutors could ensure the panel had a chance to consider testimony that could be seen as exculpatory. It was uncertain if more witnesses might be summoned. But authorities mindful of the deadly riot by Trump supporters at the US Capitol on 6 January 2021 took steps to prepare for any violence that could accompany the unprecedented prosecution of a former president. All New York police department officers were expected to be in uniform and ready for deployment, media outlets reported. Trump responded on his Truth Social platform, complaining that NYPD officers would be used to “put their greatest champion and friend in prison” while the “Soros-backed DA allows murderers and other violent criminals to freely roam the sidewalks of New York”. CNN said law enforcement officials were treating Tuesday as a “high alert day”, though they had seen no credible threat. A telephoned bomb threat delayed a hearing in a separate case involving Trump, a $250m state civil suit over his business practices in another lower Manhattan court. CNN also said police in Washington were “not currently tracking any direct or credible threats to the US Capitol”, according to an internal intelligence assessment. Informed sources expected a grand jury would vote on an indictment on Wednesday, with an announcement on Thursday or Friday. Trump is due to hold his first large-scale rally of the 2024 Republican primary in Waco, Texas, on Saturday. Media outlets reported a likely surrender to authorities in New York on Monday. A Trump campaign insider told the Guardian on Monday Trump would not resist extradition from Florida to New York. Monday’s testimony to the grand jury came from Robert Costello. A lawyer with close ties to key Trump aides, Costello was invited by prosecutors after saying he had information to undercut the credibility of Michael Cohen, the former Trump lawyer who became a key witness in the Manhattan investigation. Costello advised Cohen after Cohen became entangled in a federal investigation into hush money payments to Daniels and another woman who claims an affair with Trump, the former Playboy model Karen McDougal, in 2018. Pleading guilty, Cohen said the payments were directed by Trump. He became a vociferous Trump critic, testifying before Congress and the Manhattan grand jury. Trump, who denies having sex with either woman, has called Cohen a liar. Speaking to reporters on Monday, Costello said he came forward because he did not believe Cohen, who pleaded guilty to federal charges including campaign finance violations related to the payments, and served time in prison, could be trusted. “If they want to go after Donald Trump and they have solid evidence, then so be it,” Costello said. “But Michael Cohen is far from solid evidence.” Cohen told MSNBC Costello was never his lawyer and “lacks any sense of veracity”. There were no clear signs Costello’s testimony affected the investigation. Cohen was available for more than two hours in case prosecutors wanted him to rebut Costello but was told he was not needed, his attorney said. The testimony came two days after Trump said he expected to be indicted and arrested and urged supporters to act, directing particularly hostile rhetoric towards Bragg. Trump claims Bragg is biased against him because he is a Democrat and because he is Black. Late on Monday, CBS News said law enforcement sources had reported a “significant increase” in “threats and violent rhetoric online from domestic violent extremists”. However, CBS also said that while officials were “continuing to monitor for credible specific threats”, they had “not identified any credible or direct threats to a person or property”.