Footage of a prototype of the traffic-straddling vehicle driving down a short track in northern Hebei province while two cars drove underneath attracted global attention in August last year.
But many doubted the project's feasibility and Chinese media questioned its sources of financing.
Beijing police on Sunday said the project's investor, the online lending firm Huaying Kailai, was being investigated in connection with illegal fundraising.
The police statement said 32 people, including a person surnamed Bai, have been detained.
The police said it was seeking to "recover the funds involved in this case and protect investors' legal rights and interests".
But police did not provide further details about the allegations.
The electric vehicle, first proposed in 2010, needed at least two lanes to operate and an additional lane to allow traffic to pass, according to TEB.
The bus was designed to carry up to 1,400 passengers at a top speed of 60 kilometres per hour (37 miles per hour), TEB has said -- although videos only showed it moving slowly.
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