Complex sentence: On 21 September 2013 ten unidentified gunmen attacked the up-scale Westgate shopping mall and then fought with Kenyan security forces in gun battles in Nairobi, Kenya, fatally shooting at least 69 people, according to the Kenyan Red Cross.
Split into simpler sentences: On 21 September 2013 ten unidentified gunmen attacked the up-scale Westgate shopping mall in Nairobi, Kenya. Militants lay siege and fought with Kenyan security forces in gun battles, fatally shooting at least 69 people, according to the Kenyan Red Cross.