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〃That's one。〃
〃Okay。 Here we go。 Laying it onto VHS。〃 Theresa started the first copy。 She ran the tape forward at high speed； the images streaky and quick。 On the side monitors； the signals bounced and jittered nervously。
She said； 〃Does this have something to do with the murder last night？〃
〃Yes。 You know about that？〃
She shrugged。 〃I saw it on the news。 The killer died in a car crash？〃
〃That's right；〃 I said。
She was turned away。 The three…quarter profile of her face was strikingly beautiful； the high curve of her cheekbone。 I thought of what a playboy Eddie Sakamura was known to be。 I said； 〃Did you know him？〃
〃No；〃 she said。 After a moment she added； 〃He was Japanese。〃
Another moment of awkwardness descended on our little group。 There was something that both Theresa and Sanders seemed to know that I did not。 But I didn't know how to ask。 So I watched the video。
Once again； I saw the sunlight moving across the floor。 Then the room lights came up as the office personnel thinned。 Now the floor was empty。 And then； at high speed； Cheryl Austin appeared； followed by the man。 They kissed passionately。
〃Ah ha；〃 Sanders said。 〃Is this it？〃
〃Yes。〃
He frowned as he watched the action progress。 〃You mean the murder is recorded？〃
〃Yes；〃 I said。 〃On multiple cameras。〃
〃You're kidding。〃
Sanders fell silent； watching events proceed。 With the streaky high…speed image； it was difficult to see more than the basic events。 The two people moving to the conference room。 The sudden struggle。 Forcing her back on the table。 Stepping away suddenly。 Leaving the room in haste。
Nobody spoke。 We all watched the tape。
I glanced at Theresa。 Her face was blank。 The image was reflected in her glasses。
Eddie passed the mirror； and went into the dark passageway。 The tape ran on for a few more seconds； and then the cassette popped out。
〃That's one。 You say there are multiple cameras？ How many all together？〃
〃Five； I think；〃 I said。
She marked the first cassette with a stick…on label。 She started the second tape in the machine； and began another high…speed duplication。
I said； 〃These copies are exact？〃
〃Oh； yes。〃
〃So they're legal？〃
Sanders frowned。 〃Legal in what sense？〃
〃Well； as evidence； in a court of law… 〃
〃Oh； no；〃 Sanders said。 〃These tapes would never be admissible in a court of law。〃
〃But if they're exact copies… 〃
〃It's nothing to do with that。 All forms of photographic evidence including video； are no longer admissible in court。〃
〃I haven't heard that；〃 I said。
〃It hasn't happened yet；〃 Sanders said。 〃The case law isn't entirely clear。 But it's ing。 All photographs are suspect these days。 Because now； with digital systems； they can be changed perfectly。 Perfectly。 And that's something new。 Remember years ago； how the Russians would remove politicians from photographs of their May Day line ups？ It was always a crude cut…and…paste job … and you could always see that something had been done。 There was a funny space between the shoulders of the remaining people。 Or a discoloration on the back wall。 Or you could see the brush…strokes of the retoucher who tried to smooth over the damage。 But anyway； you could see it … fairly easily。 You could see the picture had been altered。 The whole business was laughable。〃
〃I remember；〃 I said。
〃Photographs always had integrity precisely because they were impossible to change。 So we considered photographs to represent reality。 But for several years now； puters have allowed us to make seamless alterations of photographic images。 A few years back the National Geographic moved the Great Pyramid of Egypt on a cover photo。 The editors didn't like where the pyramid was； and they thought it would pose better if it was moved。 So they just altered the photograph and moved it。 Nobody could tell。 But if you go back to Egypt with a camera and try to duplicate that picture； you'll find you can't。 Because there is no place in the real world where the pyramids line up that way。 The photograph no longer represents reality。 But you can't tell。 Minor example。〃
〃And someone could do the same thing to this tape？〃
〃In theory； any video can be changed。〃
On the monitor； I watched the murder occurring a second time。 This camera was from the far end of the room。 It didn't show the actual murder very well； but afterward； Sakamura was clearly visible as he walked toward the camera。
I said； 〃The image could be changed how？〃
Sanders laughed。 〃These days； you can make any damn change you want。〃
〃Could you change the identity of the murderer？〃
〃Technically； yes；〃 Sanders said。 〃Mapping a face onto a plex moving object is now possible。 Technically possible。 But as a practical matter； it'd be a bitch to do。〃
I said nothing。 But it was just as well。 Sakamura was our leading suspect and he was dead； the chief wanted the case finished。 So did I。
〃Of course；〃 Sanders said； 〃the Japanese have all sorts of fancy video algorithms for surface mapping and three…dimensional transformations。 They can do things that we can't begin to imagine。〃 He drummed his fingers on the table again。 〃What is the timetable of these tapes？ What's their history？〃
I said； 〃The murder happened at eight…thirty last night； as shown on the clock。 We were told the tapes were removed from the security office around eight forty…five p。m。 We asked for them； and there was some back…and…forth with the Japanese。〃
〃As always。 And when did you finally take possession？〃
〃They were delivered to division headquarters around one…thirty a。m。〃
〃Okay；〃 Sanders said。 〃That means they had the tapes from eight forty…five to one…thirty。〃
〃Right。 A little less than five hours。〃
Sanders frowned。 〃Five tapes； with five different camera angles； to change in five hours？〃 Sanders shook his head。 〃No way。 It just can't be done； Lieutenant。〃
〃Yeah；〃 Theresa said。 〃It's impossible。 Even for them。 It's just too many pixels to change。〃
I said； 〃You're sure about that。〃
〃Well；〃 Theresa said； 〃the only way it could be done that fast is with an automated program； and even the most sophisticated programs need you to polish the details by hand。 Things like bad blur can give it all away。〃
〃Bad blur？〃 I said。 I found I liked asking her questions。 I liked looking at her face。
〃Bad motion blur；〃 Sanders said。 〃Video runs at thirty frames a second。 You can think of each frame of video as a picture that's shot at a shutter speed of one…thirtieth of a second。 Which is very slow … much slower than pocket cameras。 If you film a runner at a thirtieth of a second； the legs are just streaks。 Blurs。
〃That's called motion blur。 And if you alter it by a mechanical process； it starts to look wrong。 The image appears too sharp； too crisp。 Edges look odd。 It's back to the Russians： you can see it's been changed。 For realistic motion； you need the right amount of blur。〃
〃I see。〃
Theresa said； 〃And there's the color shift。〃
〃Right；〃 Sanders said。 〃Inside the blur itself； there is a color shift。 For example； look there on the monitor。 The man is wearing a blue suit； and his coat is swinging out as he spins the girl around the room。 Now。 If you take a frame of that action；