KYIV, Ukraine—A Belarusian activist living in exile in Ukraine was found hanged in a park near his home in Kyiv early on Tuesday, and Ukrainian police said they had launched a murder case. Vitaly Shishov, who led a Kyiv-based organization that helps Belarusians fleeing persecution, had been reported missing by his partner on Monday after failing to return home from a run. Police said they had launched a criminal case for suspected murder, including investigating whether attackers had tried to disguise the killing as suicide. Shishov, 26, had felt under constant surveillance since he left Belarus last year after taking part in anti-government protests, his colleagues said. He had been warned about possible threats, including being kidnapped or killed. Ukraine, Poland, and Lithuania have become havens for Belarusians during a crackdown by President Alexander Lukashenko following a disputed election last year. Tens of thousands of people have been detained and …