Honolulu police are investigating an assault on Oahu environmental activist Carroll Cox while he was looking into the alleged toxic dumping and misuse of land under the state Department of Hawaiian Home Lands.

Cox said he was taking photographs of a modular house on Hawaiian Homes land from inside his car near Boxer Road in Kalaeloa on Tuesday afternoon when a masked man struck him on the head with what felt like an iron pipe and another masked man entered his vehicle from the passenger side and stole his car keys.

"They were trying to murder me," Cox said. "You don’t hit people on the head with an iron pipe."

Cox, who filed a police report, said his recollection of incidents after the attack was sketchy and he thinks he was unconscious for a time.

He said he doesn’t know who attacked him.

Cox said he had bruises on his arm and knees and required nine staples to close a wound to the left side of his head.

In a Tuesday email to DHHL Director Jobie Masagatani, Cox charged that the modular home was put on Hawaiian Homes land in Kalaeloa without proper authorization.

Cox, interviewed Wednesday, said illegal dumping of calcium hydroxide used for paving roads has also occurred on nearby Hawaiian Homes lands.

Hawaiian Homes spokesman Punialoha Chee said the department is looking into the charges.

"Mr. Cox has made a number of allegations, which we are looking into," Chee said. "We take all these very seriously."

Chee said the modular house was removed Tuesday because it wasn’t authorized by the Hawaiian Homes Commission.

Chee said his understanding was that transportation trucking official Mark Aiwohi planned to seek a revocable permit for the modular house to be on the Hawaiian Homes land and that the modular house was put there temporarily.

But Aiwohi was unable to get the revocable permit because the commission has been reviewing the permit process, Chee said.

Aiwohi was unavailable for comment.