* Islamist sect Boko Haram behind similar past incidents
* Attacks continue in face of military crackdown
* Boko Haram is country's biggest security threat (Updates death toll, adds witness quote)
By Lanre Ola and Ibrahim Mshelizza
MAIDUGURI, Nigeria Jan 14 (Reuters) - A car bomb killed at least 29 people on Tuesday in Nigeria's northeastern city of Maiduguri, the epicentre of an ...