This information should be disclosed prior to the sale of a home. Your agent should ask the sellers agent. You don't want to speak to the sellers directly, have your agent help you with this matter.
This is a very iffy question. A seller must disclose anything that might affect the value of the property. It is generally accepted that if a death happened in the last 3 years, or there was a gruesome death, ie murder etc. it should be disclosed. The law is very vague and the best answer, as a selling agent, is to just disclose it. Having said all that, ask the listing agent, or better yet your buyer's agent to find out.