A 42-year-old Tokyo schoolteacher who allegedly planted a handmade bomb in a high school in Tokyo's Minato Ward earlier this month was served a fresh arrest warrant Monday on charges of attempted murder and violation of the explosives control law, police sources said.

Kotaro Matsumura, a math teacher at Hiroo High School in the ward, has already been arrested and charged with inflicting injury after placing an explosive in the principal's office of nearby Mita High School on March 12.

Matsumura sprayed tear gas on a Mita High School official who got in his way, police said. The official was hospitalized with an eye injury.

On Monday, police served Matsumura a fresh warrant for attempted murder after the bomb was judged capable of killing people, and because of his confession that he intended to kill the principal, police sources said.

The bomb exploded later in the day while a special police unit was attempting to dispose of it. Police sources said Matsumura made the explosive at his house in Toda, Saitama Prefecture, by stuffing black powder and lead balls into a stainless steel pipe around March 5. He crept into Mita High School to plant the bomb, which was in a paper box, on the desk of Principal Hiroshi Okamoto, they added.

Matsumura reportedly told investigators that he made the bomb by referring to war movies, and that he felt discriminated against by his school in terms of pay.

He said he tried to kill the principal of nearby Mita High School, whom Matsumura claims has the same attitude as the Hiroo High School principal, because he thought targeting the principal of his own school would be "too obvious," police sources quoted him as saying.