The U.K. Serious Fraud Office (SFO) carried out several residential raids Wednesday as it announced the launch of a criminal investigation into collapsed property investment firm Signature Group.

The SFO coordinated with the National Crime Agency in arresting four unnamed individuals in connection with the probe, which seeks to determine how Signature Group entered administration with losses of up to 140 million pounds (U.S. $177 million) impacting approximately 1,000 investors across the globe.

“We have people up and down the country left out of pocket and buildings left derelict at the center of our cities,” said SFO Director Nick Ephgrave in an agency press release. “Today’s arrests and searches will help us reconstruct exactly what happened. This is now an active criminal investigation.”

Signature Group operated for more than seven years and bought historic U.K. buildings for redevelopment into luxury hotels, residential apartments, and office spaces. Investors were promised returns on their investment of between 8 and 15 percent, the SFO noted.

The company entered administration in 2020.

The investigation is the fourth launched by the SFO since Ephgrave took over as director at the end of September. In a speech earlier this month, he promised the agency would lean heavier on dawn raids to open cases.

“This provides momentum to the investigation: it gets people in an interview room, you look them in the eye and start asking questions, put them under some pressure, search the house, [and] crack the evidence. Why wait?” he said.