Given the following context:  In September 1930 Heseltine moved with Barbara Peache into a basement flat at 12a Tite Street in Chelsea. With no fresh creative inspiration, he worked in the British Museum to transcribe the music of English composer Cipriani Potter, and made a solo version of "Bethlehem Down" with organ accompaniment. On the evening of 16 December Heseltine met with Van Dieren and his wife for a drink and invited them home afterwards. According to Van Dieren, the visitors left at about 12:15 a.m. Neighbours later reported sounds of movement and of a piano in the early morning. When Peache, who had been away, returned early on 17 December, she found the doors and windows bolted, and smelled coal gas. The police broke into the flat and found Heseltine unconscious; he was declared dead shortly afterwards, apparently as the result of coal gas poisoning.An inquest was held on 22 December; the jury could not determine whether the death was accidental or suicide and an open verdict was returned. Most commentators have considered suicide the more likely cause; Heseltine's close friend Lionel Jellinek and Peache both recalled that he had previously threatened to take his life by gas and the outline of a new will was found among the papers in the flat. Much later, Nigel Heseltine introduced a new theory—that his father had been murdered by Van Dieren, the sole beneficiary of Heseltine's 1920 will, which stood to be revoked by the new one. This theory is not considered tenable by most commentators. The suicide theory is supported (arguably), by the (supposed, accepted) fact that Heseltine/Warlock had put his young cat outside the room before he had turned on the lethal gas.Philip Heseltine was buried alongside his father at Godalming cemetery on 20 December 1930. In late February 1931, a memorial concert of his music was held at the Wigmore Hall; a second such concert took place in the following December.In 2011 the art critic Brian Sewell published his memoirs, in which he claimed that he was Heseltine's illegitimate son, born in...  answer the following question:  What is the last name of the person whose death could not be determined to be accident or suicide?
A:
Heseltine