Police said 14 men and one woman were detained over their purchases of Next Digital shares last month, the company that owns Hong Kong’s pro-democracy Apple Daily newspaper.

Next Digital’s shares soared more than 1,000% in the two days after the Aug 10 arrest of its owner Jimmy Lai — as well as senior company executives — under Beijing’s new national security law.

Apple Daily’s newspaper offices were raided the same day.

Lai and his executives are accused of “colluding with foreign forces”, although no charges have yet been formally brought.

The arrests and raid sparked online calls by supporters to buy Next Digital shares as a show of support for a paper stridently critical of Beijing.

Most of those gains have since been wiped after Hong Kong’s securities regulator advised traders to exercise “extreme caution” and after Lai himself called on his supporters to avoid buying.

Thursday’s investigation was announced by city police and not the Securities and Futures Commission, the stock market regulator.

Officers said the 15 people were arrested on suspicion of “conspiring to defraud” as well as “handling criminal profits”.

The group included at least one person with links to “triad” organised crime gangs as well as six unemployed people.

Investigators said the group allegedly acted in concert to make 13,200 transactions involving over 1.69 billion shares of Next Digital between Aug 10-12 — accounting for 24% of the shares traded over that period.

The transactions allegedly netted the group HK$38.7 million (US$5 million) in profit, of which more than HK$25 million went to one person.

“Their orders for buying and selling had a guiding effect, they bought in together at coincidentally the same price,” superintendent Chow Cheung-yau told reporters, saying the group’s activity was not the same as legal market speculation.

News of the arrests sent Next Digital’s shares see-sawing once more on Thursday.

After initially plunging, shares spiked as much as 97% up.

They ended the day 37% up at HK$0.41.