South Korea's special investigation team has raided the offices of the Seoul Metropolitan Police Agency. It's part of a probe into last weekend's crowd crush -- one of the country's deadliest disasters.

The search comes a day after police admitted several people called them with concerns about the crowd in the hours before the chaos. South Korean news outlets report eight locations were raided by national police Wednesday. They include the Yongsan Ward Office and the local fire department.

Tens of thousands partied in the Itaewon District Saturday night. As people surged forward, many were crushed leaving 156 dead and more than 150 others injured.

People are raising concerns about street design in the area. News outlets are reporting an illegally constructed terrace part of a restaurant may be one of the factors that contributed to the crush. Some experts say it made the street even narrower.

Authorities reportedly urged the restaurant last year to fix the structure but it did not happen. They say several other illegal structures in the neighborhood may have narrowed roads leading up to the site of the crush, hindering rescue operations.