Singer 's plane was flying at more than 600 mph when it began to plummet , official says . It could have plunged at 28,000 feet , the transportation secretary says . Determining what caused the crash in northern Monterrey could take Wednesday . Pedro Rivera Jr. , one of the singer 's brothers , said the family was waiting to read a document detailing her wishes that she had left with a sister about a month ago . Some of Jenni 's family members believe she could be alive .
Singer 's plane was flying at more than 600 mph when it began to plummet , official says . It could have plunged at 28,000 feet , the transportation secretary says . Determining what caused the crash in northern Monterrey could take Wednesday . Some of Jenni 's family members believe she could be alive .