BEIJING — Central investigators have detained at least two senior police officials with close ties to Wang Lijun, the former police chief of Chongqing who set off a national political scandal by confiding suspicions of a murder plot to US officials, according to people with police contacts there.

A third police official also close to Wang has been dismissed. The moves are a sign that the inquiry into Wang could be reaching a critical phase.

The two detained police officials are Tang Jianhua, the city’s deputy police chief, and Wang Pengfei, former department head of the Yubei district. Both were escorted out of Chongqing in June by security officers on the orders of the Central Discipline Inspection Commission, the Communist Party’s anticorruption body and one of the lead agencies in the far-reaching inquiries into Wang Lijun and Bo Xilai, the former party chief of Chongqing and a deposed Politburo member.

Wang Pengfei, who appears to have no family ties to Wang Lijun, was removed from his post June 25 as head of the Yubei District Police Department, according to Xinhua, the state news agency. The same day, Li Yang, head of the criminal investigations division, was also dismissed.

Wang Pengfei and Li both followed Wang Lijun from the northeast province of Liaoning to take posts in Chongqing after Wang Lijun was appointed police chief of Chongqing by Bo. Together, the men carried out a campaign against what they called at the time organized-crime gangs; the campaign also involved persecutions of private businesspeople and enemies of Bo and his allies, and is now being widely criticized.

Wang Pengfei is also a wiretapping specialist believed to be involved in a wide-ranging wiretapping campaign run by the police chief and Bo. And he arranged a car in February for the police chief to use in a secret trip to a nearby US consulate, a visit that catalyzed the scandal, say two people with police contacts in Chongqing.

Political observers in Chongqing and Beijing say Wang Lijun’s trial could start as early as this month. One person said he had heard that the trial could take place in Anhui province, in central China, although it was not obvious why that setting was an option.

Wang Lijun could be charged with treason, although some of the observers say party officials may decide to show leniency because he has been helping with the investigations into the Bo family.

The recent detentions of police officials close to Wang Lijun could also indicate that Wang Lijun will face charges related to the so-called crime crackdown called the ‘‘strike black’’ campaign, which began in June 2009 and reportedly involved the torture of many people.