As well as the deaths, more than 80 people were injured when two commuter trains slammed into each other on a single-line track near Bad Aibling, 60 kilometers (40 miles) southeast of Munich, early on Feb. 9.
Prosecutor Wolfgang Giese said his office has opened a criminal investigation against the 39-year-old dispatcher on suspicion of negligent homicide, bodily harm and interference with rail traffic.
"Had he (the dispatcher) behaved according to the rules, the trains would not have collided," Giese said. He didn't identify the man, who was interviewed by police Monday in the presence of his lawyer.
The two trains were supposed to pass each other at a station where the track was divided, but instead they crashed head-on in a curve.
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Giese said a technical failure of the trains or signaling equipment had been ruled out, but investigators plan to reconstruct the accident to test their theory of what happened.
Fellow prosecutor Juergen Branz said there was no indication the dispatcher was under the influence of alcohol or drugs at the time of the crash.
If convicted the dispatcher could face up to five years in prison.