Complex sentence: The latter two incidents are generally considered to have been minor, in that they caused no loss of life other than those of the perpetrators and appear not to have been planned in advance; in the first attack, however, three bystanders were killed.
Split into simpler sentences: The latter two incidents are generally considered to have been minor, in that they caused no loss of life other than those of the perpetrators and appear not to have been planned in advance. In the first attack, however, three bystanders were killed.