A branch office head of Tokyu Construction Co. has committed suicide after being questioned by prosecutors in connection with alleged tax evasion by engineering firm Mizutani Kensetsu Co., sources said late Thursday.

The chief of Tokyu Construction's Tohoku branch in Sendai is believed to have killed himself Tuesday after having been questioned by the Tokyo District Public Prosecutor's Office several times, the sources said. His name has been withheld.

In reaction to the news, Shuji Iwamura, deputy chief of the prosecutor's office, expressed condolences over his death but would not reveal the circumstances leading up to his suicide, including how the questioning was conducted.

Prosecutors suspect Mie Prefecture-based Mizutani Kensetsu hid more than 3.8 billion yen in taxable income during two business years through August 2004.

They also believe the money gained in tax evasion scams may have gone to the political community and underworld syndicates.

Prosecutors are making efforts to examine the money flow because an allegation has been made that Mizutani Kensetsu amassed slush funds for political lobbying.

The probe apparently involves a dam project financed by Fukushima Prefecture.