I transcribed portions from the video statements police issued in order to get a better idea of the timeline. Feel free to add anything else you find important. All the videos are on the Bullhead City, Arizona Government FB page.
https://www.facebook.com/pages/Bullhead-City-Arizona-Government/343118996584?hc_location=timeline
September 2, ~9 am. police statement, Chief Williamson speaking:
"The residents there reported that Isabella Grogan-Cannella, an eight year old girl, was missing, she was no longer in her bed or anywhere to be found in the residence. Since that time we've been involved in a very active search for Bella. [gives description].
The police department, the police auxiliary and the fire department have been actively searching and canvassing the neighborhood, nearby parks and river. Since very early this morning a Care Flight helicopter has assisted us in a search from the air.
We currently have a large amount of resources from the Federal Bureau of Investigation on site and more coming. We have the National Center for Missing and Exploited Children on site to assist us with this investigation.
The Mohave County Sheriff's office Search and Rescue is out, assisting us actively with this search and many more agencies have pledged assistance when, and should we need it."
[He then asks the public to look for Bella. A disclaimer was published stating that an Amber Alert wasn't issued as there was no significant information that an abduction has occurred.]
September 3 public update, 10:30 am., Chief Williamson speaking:
"We are continuing our search for Bella, by searching the Colorado river, by land and by boat and by... with air resources. We are also conducting door to door searches, area searches.
We have a criminal investigation that is underway."
[The chief goes on to ask everyone to search around their homes and to call in tips, no matter how unimportant they may seem.]
September 3 Press Conference, ~4:45 pm., Chief Williamson speaking:
"At about 1:30 am. On Tuesday morning Bella's family reported her missing from her residence. There were no signs of forced entry or a struggle.
Since there was [sic] no witnesses or evidence that an abduction occurred, this incident did not meet the criteria for an Amber Alert. However, an abduction has not been ruled out and detectives, with the assistance of the FBI, the National Center for Missing and Exploited Children and other law enforcement agencies have been working diligently to uncover what happened to Bella."
September 4, 1:40 pm., police press conference, Chief Williamson speaking:
[Announces Justin Rector's arrest.]
"Rector is a family friend and it's reported that he stayed at that residence for a few days.
[
]
Bella's 10 year old sister told police that the last time she saw Bella was about 11:30 pm. on Monday when she went to the bathroom. When... her sister reported that Bella was with Rector and when she came out of the bathroom they were gone.
Bella's sister did not hear any yelling or any kind of disturbance."
[
]
He answers questions:
"Ralph is the boyfriend of the mother, that's the relationship, the best way to describe the relationship.
There were several people at the house, uh, living at the house and staying in the house at that time and I do not have the list of all those names with me."