Satoshi Uematsu exhibited disturbing behavior before Tuesday's massacre at a care home, delivering an ominous euthanasia letter to House of Representatives Speaker Tadamori Oshima and telling co-workers and the police he intended to kill disabled people, prompting his forced hospitalization.

But despite obvious signs the suspect posed a risk to those in his charge, 19 people at the Tsukui Yamayuri En facility were murdered and 26 were injured, leaving the public and authorities wondering whether more could have been done to stop him.

"I hope the world will become more peaceful," Twitter user @tenka333 — thought to be Uematsu — tweeted at 2:50 a.m. Tuesday, around the time he was stalking the halls of the care home, slashing the necks of residents as they slept.