The bomb killing Ukrainian prisoners detonated within the building. The roof was mostly intact, as this image makes clear: https://duckduckgo.com/?q=Ukraine+Olenivka+prison+killed+by+bomb&atb=v310-1&iar=images&iax=images&ia=images&iai=https%3A%2F%2Fs.yimg.com%2Fny%2Fapi%2Fres%2F1.2%2FLL5Zowr_jMSYHkRtWXHUiQ--%2FYXBwaWQ9aGlnaGxhbmRlcjt3PTk2MDtoPTU0MA--%2Fhttps%3A%2F%2Fs.yimg.com%2Fuu%2Fapi%2Fres%2F1.2%2FLPhcDw._hREYH15p1hLvwQ--~B%2FaD01NzY7dz0xMDI0O2FwcGlkPXl0YWNoeW9u%2Fhttps%3A%2F%2Fmedia.zenfs.com%2Fen%2Feuronews_uk_articles_973%2Ff0410fd9fb3086466d3a0f16728f00ed.

So far as I know a HIMARS rocket cannot burrow underground and detonate below a building. This makes your post another example of Russian useful idiocy, as defined by the KGB defector Yuri Bezmenov (http://romaninukraine.com/wp-content/uploads/2017/10/22136936_1462335407206791_7032462528501845579_o.jpg)